1. Field of the Invention
The present invention relates to a piezoelectric component, and more particularly, a piezoelectric component such as an oscillator, a discriminator or a filter incorporating a piezoelectric resonator.
2. Description of the Related Art
FIG. 20 is a diagram showing an example of a piezoelectric component relating to the present invention. A piezoelectric component 101 includes a substrate 102. As shown in FIG. 21, pattern electrodes 103a and 103b are disposed on the substrate 102 and supporting members 104 formed of an electroconductive material located on external electrodes 106a and 106b of a piezoelectric component 105 are attached on the pattern electrodes 103a and 103b via bonding or similar process. For example, the piezoelectric resonator 105 includes a base member 105a in which a plurality of piezoelectric layers and electrodes are laminated. The two external electrodes 106a and 106b extending in the longitudinal direction are located on one side surface of the base member 105a and are connected to the electrodes of the base member 105a. The piezoelectric layers are polarized along the longitudinal direction of the base member 105a. A signal is supplied between the external electrodes 106a and 106b to apply electric fields in the longitudinal direction of the base member 105a. The electric fields cause the piezoelectric layers to expand and contract, thus exciting fundamental vibration in the base member 105a in the longitudinal direction.
A silicone resin 107 or the like is applied to upper and lower surfaces of the piezoelectric resonator 105. A substrate 102 is covered by a cap 108 so as to cover the piezoelectric resonator 105. In this piezoelectric component 101, a signal is input between the pattern electrodes 103a and 103b to generate fundamental vibration of longitudinal vibration in the piezoelectric resonator 105. The piezoelectric resonator 105 caused to vibrate in this manner has its mechanical quality factor Qm adjusted by the application of silicone resin 107 to the piezoelectric resonator 105 which increases the vibration load on the piezoelectric resonator 105.
In the piezoelectric component 101 shown in FIG. 20, however, there is a possibility of water vapor entering inside the cap 108 through the adhesive between the insulating substrate 102 and the cap 108 and condensing on the surface of the piezoelectric resonator and so on due to a change in temperature. In such a case, when the piezoelectric component 101 is mounted by reflow soldering, condensed water vaporizes to abruptly increase the atmospheric pressure inside the cap 108, thereby producing a force which lifts the cap 108. Such a force may cause the cap 108 to come off or be removed from the substrate 102.
In addition, a sufficient amount of silicone resin 107 cannot be supplied because of spreading and running of silicone resin 107 at the time of application of silicone resin 107, resulting in a failure to accurately adjust Qm of the piezoelectric resonator to the desired value. In the case where a ladder filter is formed by using, for example, four piezoelectric resonators as shown in FIG. 22, a variation in the amount of silicone resin 107 occurs between piezoelectric resonators 105 due to spreading and running of silicone resin 107, and the desired Qm of each resonator cannot be obtained.
Further, since silicone resin 107 is supplied before covering the resonator(s) with the cap 108 in the piezoelectric component 101 constructed as described above, silicone resin 107 is interposed between the substrate 102 and the cap 108 if the resin 107 spreads to the cap attachment portion of the substrate 102. In such a situation, cap attachment failure results. To avoid such a failure, it is necessary to increase the size of the substrate 102 by an amount which is larger than an area through which the silicone resin 107 can spread. Because of this problem, it has been difficult to reduce the size of the piezoelectric component 101.